Hello, first great plugin! But, how you can read in the topic, I have a startup error since Bukkit RB#1317.
I hope you go to fix this soon:
[SEVERE] Error occurred while enabling SimpleClans v1.7.3 (Is it up to date?): Cannot store null
java.lang.IllegalArgumentException: Cannot store null
at org.bukkit.configuration.MemorySection.prepForStorage(MemorySection.java:526)
at org.bukkit.configuration.MemorySection.set(MemorySection.java:189)
at org.bukkit.configuration.MemorySection.set(MemorySection.java:191)
at net.sacredlabyrinth.phaed.simpleclans.managers.SettingsManager.save(SettingsManager.java:294)
at net.sacredlabyrinth.phaed.simpleclans.managers.SettingsManager.load(SettingsManager.java:232)
at net.sacredlabyrinth.phaed.simpleclans.managers.SettingsManager.(SettingsManager.java:115)
at net.sacredlabyrinth.phaed.simpleclans.SimpleClans.onEnable(SimpleClans.java:71)
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:170)
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:957)
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:280)
at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:171)
at org.bukkit.craftbukkit.CraftServer.enablePlugins(CraftServer.java:154)
at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:297)
at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:284)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:152)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:348)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)

Try this version and let me know if it fixes the problem:

http://sacredlabyrinth.net/releases/SimpleClans.jar

The link is dead...

The error still occurs (Used your version from the link):
[SEVERE] Error occurred while enabling SimpleClans v1.7.3 (Is it up to date?): Cannot store null
java.lang.IllegalArgumentException: Cannot store null
at org.bukkit.configuration.MemorySection.prepForStorage(MemorySection.java:526)
at org.bukkit.configuration.MemorySection.set(MemorySection.java:189)
at org.bukkit.configuration.MemorySection.set(MemorySection.java:191)
at net.sacredlabyrinth.phaed.simpleclans.managers.SettingsManager.save(SettingsManager.java:292)
at net.sacredlabyrinth.phaed.simpleclans.managers.SettingsManager.load(SettingsManager.java:230)
at net.sacredlabyrinth.phaed.simpleclans.managers.SettingsManager.(SettingsManager.java:115)
at net.sacredlabyrinth.phaed.simpleclans.SimpleClans.onEnable(SimpleClans.java:71)
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:170)
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:957)
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:280)
at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:171)
at org.bukkit.craftbukkit.CraftServer.enablePlugins(CraftServer.java:154)
at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:297)
at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:284)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:152)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:348)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)

oops, typo. try again.